1. Field of the Invention
The invention relates to a method for adjusting a pull resistor on a contact terminal of an electronic module, in particular an Application Specific Integrated Circuit (ASIC), arranged on a printed circuit board after initiating a restart of the electronic module which, during a run-up process, changes the electronic module from a switched-off state into a switched-on state.
2. Description of the Related Art
Electronic modules which, in most cases, form part of an electronic component group and which are soldered to a wiring support that is referred to herein as a printed circuit board (PCB). Here, they form a structural and generally also functional unit comprising integrated and/or discrete and passive components with the other components of the electronic component group, which are connected electrically and mechanically via a line network to the printed circuit board. Here, the electronic module includes a plurality of contact lines, which each extend from contact terminals of the electronic module, which comprise populated and unpopulated contact terminals due to the logical programming, via soldered connections to the printed circuit board. The contact lines are continued on the printed circuit board as conductor paths, where they can lead for instance to another electronic component, such as another electronic module or an interface module.
The signal and voltage supply terminals of the electronic module are understood to be contact terminals, which are connected via what are known as bond wires to the soldered connections to the printed circuit board. With Ball Grid Arrays (BGAs) and Flip-Chip Ball Grid Arrays (FCBGAs), the soldered connections are solder balls (balls), via which the BGA housing or the FCBGA housing is fastened to the printed circuit board. With Quad Flat Packages (QFPs), what are known as pins are soldered to the printed circuit board, which are each uniquely assigned to the contact terminals, where the terms “pins” and “balls” are in practice used interchangeably because, for instance, with ASICs the package can be, within certain limits, selected freely.
Within the module, the contact terminals are generally connected to input/output I/O buffers, which are arranged at the output of the electronic module and which drive the relevant contact line with its specific physical behavior.
On account of complex multiplex methods for different applications, electronic modules, in most cases, offer different interfaces on the same contact terminal (“Pin”), such as with an Serial Peripheral Interface (SPI) or with Universal Asynchronous Receiver/Transmitter (UART). On account of their I/O characteristics, in other words, whether they are operated exclusively as an input, exclusively as an output or bi-directionally, and the interface characteristics, i.e., depending on the interface protocol or low/high active operation, these various interfaces require a different protective circuit due to pull-up resistors or pull-down resistors. For financial reasons, these pull resistors are not integrated onto the circuit board but instead within the electronic module.
The adjustment of these resistors, i.e., the activation or deactivation of a pull-up resistor or a pull-down resistor at a particular contact terminal, can be changed by corresponding software registers in the electronic module as a function of the configuration of the pin multiplexing. In the case of a restart of the electronic module (“Reset”), such as during the switch-on process or when actuating a reset button, this adjustment is however again reset to an initial value (“default value”) which is predetermined by default. A power-on reset, for example, is triggered by an internal reset circuit if the operating voltage drops below a limit value, and when the power supply is switched on. In particular, all I/O registers are also set to their initial value during a reset. The last current value for the activation or deactivation of a pull resistor at a contact terminal, which can also differ from the default value, is firstly lost until a desired adjustment of the pull resistors was/is performed again by the software of the electronic module. During the time period from the end of the run-up process until activation of a desired adjustment, an unwanted adjustment of a pull resistor is however sometimes active, which may result in malfunctions. In safety-critical applications, such a malfunction may be fatal.
Conventionally redundant pull resistors are therefore arranged on the printed circuit board depending on the application, with the pull resistors nevertheless resulting in additional costs.